Amnestic Mild Cognitive Impairment

This post is based on an important book by Scott D. Slotnick titled “Cognitive Neuroscience of Memory.” Remember to consult the website http://www.brainfacts.org/
to see the anatomical information referred to in this post.

Amnestic mild cognitive impairment (aMCI) occurs in a small but significant percentage of adults who are older than 60 years of age, with incidence increasing as a function of age. Approximately 50% of these cases will become Alzheimer’s sufferers. Individuals with aMCI have a selective impairment in long-term memory as compared to healthy age-matched control participants, and are unimpaired in other cognitive domains. There is an increasing body of evidence indicating that the long-term memory impairment in aMCI patients is due to atrophy of medial temporal lobe sub regions that is increased by a paradoxical increase in fMRI activity within the medial temporal lobe.

Structural MRI was used to compare the size of the hippocampus and the entorhinal cortex in aMCI patients and control participants. aMCI patients had a smaller hippocampal value and a smaller entorhinal cortex volume in both hemispheres as compared to age-matched control participants, indicating atrophy of these regions. In addition, the white matter pathway between the entorhinal cortex and the hippocampus had a smaller volume in aMCI patients than control participants, and this was the only white matter region in the entire brain that differed in volume. These results indicate that the long-term memory impairments in aMCI patients are due to isolated atrophy in the entorhinal cortex and the hippocampus.

A relatively higher magnitude of fMRI activity within the CA3/DG sub-region during a pattern separation task reflects a non-compensatory change in processing related to neural disruption in aMCI patients.

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